In recent years, car navigation apparatuses which guide a driver while displaying a map, mobile phones which can use a map information service, servers which provide a map information service via the Internet, etc. have been increasing. These pieces of equipment and servers hold various map databases, and provide users with information about points which they desire, i.e., so-called POI (Point Of Interest) information, on the basis of latitude and longitude data which are stored in those map databases.
Because a map database held by each equipment is based on a closed system (Closed System) and the maker and the creation year of a map database which is used by the same type of equipment are identical, there is neither displacements in the location of a POI nor variations in the expression of a POI. However, when exchange and distribution of map information and location information are carried out between equipment holding a map database and other equipment, particularly other equipment which uses a different maker's map database, because this system is an open system (Open System), there may be a case in which a displacement occurs in the location of a POI or a variation occurs in the expression of a POI according to the difference between the map databases used by those pieces of equipment, and the POI is shown as a different location or a different expression in spite of indicating the same point.
Furthermore, even in a case in which the same maker's map database is used, when the creation year of the map database differs, a change occurs in the relative relation between a POI and roads due to new construction of a building, new construction or change of a road, or the like, that is, a change occurs in the access to the POI or in the name of the POI. As a result, there is a case in which even if a POI shows the same point, the location or name of the POI differs according to the creation year of the map database.
For example, in the VICS (Vehicle Information and Communication System), in a case in which a road is constructed newly or changed, addition of a new node number and a link number or replacement of a node number and a link number are performed on the map database of the VICS. When a node number and a link number are changed in the VICS, there will be a necessity to update each maker's map database. Because new construction and change of roads are continuously made over the future, and therefore maintenance of the original map database and change of each maker's map database become a matter of necessity as long as the method of changing the original map database by performing addition or replacement of a node number and a link number is adopted, there is a problem that a large amount of work and a cost carried by this work must be supplied permanently.
In order to solve this problem, patent reference 1 discloses a location information transmission method of being able to transmit location information on a digital map without having an excessive load of maintenance. In accordance with this location information transmission method, an information provision side, in order to inform a road location, transmits both road shape data comprised of a series of coordinates indicating the road geometry of a road section of a predetermined length including that road location, and relative data indicating a road location within this road section, and a receive side which receives these pieces of information performs shape matching, specifies the road section on the digital map, and determines the road location within the road section by using the relative data.
According to the location information transmission method disclosed by this patent reference 1, even if neither node numbers nor link numbers are defined, the information provision side simply provides road shape data indicating the geometry of a road in the form of a series of coordinates so that the receive side can determine the location of the road. This location information transmission method can be used for exchange of traffic information between traffic information collection centers, provision of traffic information from either an FM station or a road beacon, and so on.
However, the location information transmission method disclosed by this patent reference 1 has a drawback of increasing the amount of data to be transmitted because the location information about the locations of many points on the road must be transmitted in order to inform the road geometry exactly. Reduction in the number of points on the road whose location information is to be transmitted to the receive side in order to remove the drawback raises the possibility of causing incorrect matching in the receive side.
To solve this problem, patent reference 2 discloses a location information transmission method of exchanging location information about locations on a digital map with a small amount of data and with a high degree of accuracy, and without having a load of maintenance. According to this location information transmission method, when transmitting a road location on the digital map, an information provision side transmits, as road location information, coordinate series information indicating the road geometry of a road section including the road location and having a length according to a situation, additional information containing at least one of attribution information about attributes of the road including the road location and detailed information about nodes within the road section, and relative information indicating the road location within the road section, and a receive side which receives this road location information performs shape matching so as to specify the road section on the digital map, and determines the road location within this road section by using the relative data.
According to the location information transmission method disclosed by this patent reference 2, the information provision side transmits the additional information, as well as the coordinate series information, to the receive side so that the receive side can specify the road geometry with a high degree of accuracy even though the amount of data of the coordinate series is small, and therefore the amount of transmission data can be reduced and the high-accuracy determination of the road location can be made by the receive side.
[Patent reference 1] JP,2001-041757,A
[Patent reference 2] JP,2001-066146,A
However, a problem which remains to be solved by the technology disclosed by above-mentioned patent reference 2 is that information about the road section, i.e., information about start and end points of the road is required and whether or not there is a match in the road location between the different map databases cannot be judged correctly. Furthermore, while the technology disclosed by patent reference 2 provides a smaller amount of information to be transmitted than the technology disclosed by patent reference 1, the technology disclosed by patent reference 2 requires a large amount of information because it needs road geometry information about many points.
In addition, the receive side needs to perform shape matching on the basis of the road geometry information transmitted thereto, and the structure of the receive side becomes complicated. A further problem is that the receive side cannot handle a large change in the shape of the road because the receive side uses the shape matching.
The present invention is made to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a location information exchange apparatus for and a location information exchange method of being able to exchange correct location information between apparatuses which have different map databases through transmission of a small amount of data in spite of having a simple structure.